In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. Image sensors are largely divided into charged coupled device (CCD) image sensor devices and CMOS image sensor devices.
A CMOS image sensor includes a photodiode section that detects radiated light and a CMOS logic circuit section that processes electrical signals to provide corresponding data. The larger the amount of light received by the photodiode section is, the better the photosensitivity characteristics of the image sensor are.
FIG. 1 is a sectional view of a CMOS image sensor according to the prior art.
According to the prior art, in order to increase photosensitivity, either the fill factor of a photodiode 11 region formed on a substrate 10 is increased, or a path of light incident to other regions outside the photodiode 11 is changed so that the light can be condensed to the photodiode 11.
A representative example of the light condensing technology is the use of microlenses 16, which are generally formed convexly of material having excellent light transmittance above the photodiodes 11, in order to refract incident light and radiate a larger amount of light onto the photodiode 11 region.
However, during the forming of the microlenses 16 according to the prior art, the miniaturized pattern leads to overlaps (A) formed between the adjacent microlenses 16 during a reflow process, whereby the overlaps (A) diminish the efficient focusing of light.
Due to recent miniaturization of microlens for CMOS image sensors (sizes of microlenses are 5.2 μm×5.2 μm, 3.2 μm×3.2 μm, and 2.5 μm×2.5 μm, respectively for CMOS image sensors of 0.25 μm-tech, 0.18 μm-tech, and 0.13 μm-tech), it is becoming increasingly important to stably secure spaces between the microlenses.